Rodents chronically exposed to high concentrations of a variety of insoluble dusts develop "lung overload" in which particle clearance, i.e., the lungs' normal ability to remove deposited dust, is impaired. If exposure continues, pathological conditions develop which are somewhat similar to the pneumoconioses which sometimes occur in workers. Extrapolation of data from rats suggests 1 to 3 grams of dust in human lungs might lead to significant impairment of particle clearance followed by disease if exposure continues. Projections indicate that current governmental limits on dust concentrations in work places may allow the mass of dust in workers' lungs to reach 1 gram in as little as 6 months of exposure. There are few techniques capable of gathering relevant data from humans to determine directly whether lung overload occurs. Magnetometry, noninvasive measurement of properties of magnetic material in a sample, is one of the few techniques which can measure the amount of dust in human lungs. Magnetometry also has the capability of monitoring several aspects of the particles' micro-environment which makes it valuable for gathering more detailed data about lung overload in animals than has been possible in previous studies. The long term objectives of the proposed research are to more fully characterize lung overload in rodents and develop methods which might be used in future human studies. The specific aims of this project are to develop a magnetic test aerosol and assemble a magnetometry system suitable for use with rodents, demonstrate that dust clearance rates can be measured as readily using magnetic aerosols as using radioactive aerosols, a technique commonly used for animals which is not readily available for humans, test hypotheses which suggest magnetometry has unique capabilities to detect lung overload, and compare results from guinea pigs with results from rats to provide a wider information base for extrapolating to humans and for planning future human studies. Animals will be exposed for 13 weeks to different amounts of a magnetic dust and an inert dust. The degree of overload will be characterized by the clearance of radioactive tracer particles and by limited histology. A variety of measurements of magnetic dust in the animals' lungs will provide the data necessary to meet the objectives of this project. Success in this project and planned subsequent human studies will lead to a better understanding of whether lung overload occurs in humans and how to set exposure guidelines to avoid adverse health effects in workers.